便携式更换 [英] Portable replacement
问题描述
您好，
我已经重写了一个函数（greater_or_equal），它依赖于
实现定义的行为和精确宽度的可用性
整数，目标是在任何平台上实现新的实现
（greater_or_equal2）。
你如何看待新的实施？
（欢迎提出意见和建议。）
int greater_or_equal（uint16_t u，uint16_t v）
{
return（int16_t）（uv）> = 0;
}
int greater_or_equal2（unsigned u，unsigned v）
{
return（（uv）& 0xffffU）< = 0x7fffU;
}
< OT>
GCC似乎理解输出以下代码的来源。
greater_or_equal2：
movl 8（％esp），％edx
cmpw％ dx，4（％esp）
setns％al
movzbl％al，％eax
ret
< ; / OT>
问候。
Hello,
I''ve rewritten a function (greater_or_equal) that relies on
implementation-defined behavior and availability of exact-width
integers, with the goal of making the new implementation
(greater_or_equal2) portable across any platform.
What do you think of the new implementation?
(Suggestions and comments are welcome.)
int greater_or_equal(uint16_t u, uint16_t v)
{
return (int16_t)(u-v) >= 0;
}
int greater_or_equal2(unsigned u, unsigned v)
{
return ((u-v) & 0xffffU) <= 0x7fffU;
}
<OT>
GCC seems to "understand" the source as it outputs the following code.
greater_or_equal2:
movl 8(%esp), %edx
cmpw %dx, 4(%esp)
setns %al
movzbl %al, %eax
ret
</OT>
Regards.
推荐答案
Noob写道：
Noob wrote:
您好，
我已经重写了一个依赖于实现定义的行为和可用性的函数（greater_or_equal）确切宽度
整数，目标是在任何平台上实现新的实现
（greater_or_equal2）。
什么你觉得新的实现吗？
（欢迎提出意见和建议。）
int greater_or_equal（uint16_t u，uint16_t v）
{
return（int16_t）（uv）> = 0;
}
int greater_or_equal2（unsigned u ，未签名的v）
{
return（（u-v）& 0xffffU）< = 0x7fffU;
}
< OT>
GCC似乎理解输出以下代码的来源。
greater_or_equal2：
movl 8（％esp），％edx
cmpw％ dx，4（％esp）
setns％al
movzbl％al，％eax
ret
< ; / OT>
Hello,
I''ve rewritten a function (greater_or_equal) that relies on
implementation-defined behavior and availability of exact-width
integers, with the goal of making the new implementation
(greater_or_equal2) portable across any platform.
What do you think of the new implementation?
(Suggestions and comments are welcome.)
int greater_or_equal(uint16_t u, uint16_t v)
{
return (int16_t)(u-v) >= 0;
}
int greater_or_equal2(unsigned u, unsigned v)
{
return ((u-v) & 0xffffU) <= 0x7fffU;
}
<OT>
GCC seems to "understand" the source as it outputs the following code.
greater_or_equal2:
movl 8(%esp), %edx
cmpw %dx, 4(%esp)
setns %al
movzbl %al, %eax
ret
</OT>
我不禁要问，它输出的是什么代码：
int greater_or_equal3（unsigned u， unsigned v）
{
return u> = v;
}
？
-
pete
I can''t help but wonder, what code does it output for:
int greater_or_equal3(unsigned u, unsigned v)
{
return u >= v;
}
?
--
pete
4月28日上午10：38 * am，Noob< root @ localhostwrote：
On Apr 28, 10:38*am, Noob <root@localhostwrote:
你好，
我已经重写了一个依赖于
实现定义的行为和精确宽度
整数的可用性，目标是使新实现在任何平台上都可移植.b $ b（big_or_equal2）。
您如何看待新的实施？
（欢迎提出意见和建议。）
int greater_or_equal （uint16_t u，uint16_t v）
{
* * return（int16_t）（uv）> = 0;
}
int greater_or_equal2（unsigned u，uns签署v）
{
* * return（（u-v）& 0xffffU）< = 0x7fffU;
}
< OT>
GCC似乎理解 ;它输出以下代码来源。
greater_or_equal2：
* * * movl * * 8（％esp），％edx
* * * cmpw * *％dx，4（％esp）
* * * setns *％al
* * * movzbl *％al，％eax
* * * ret
< / OT>
问候。
Hello,
I''ve rewritten a function (greater_or_equal) that relies on
implementation-defined behavior and availability of exact-width
integers, with the goal of making the new implementation
(greater_or_equal2) portable across any platform.
What do you think of the new implementation?
(Suggestions and comments are welcome.)
int greater_or_equal(uint16_t u, uint16_t v)
{
* *return (int16_t)(u-v) >= 0;
}
int greater_or_equal2(unsigned u, unsigned v)
{
* *return ((u-v) & 0xffffU) <= 0x7fffU;
}
<OT>
GCC seems to "understand" the source as it outputs the following code.
greater_or_equal2:
* * *movl * *8(%esp), %edx
* * *cmpw * *%dx, 4(%esp)
* * *setns * %al
* * *movzbl *%al, %eax
* * *ret
</OT>
Regards.
你仍然使用2字节掩码，如果unsigned u代表32位怎么办？
Suresh M. Shenoy
You still use a 2 byte mask, what if unsigned u represents 32 bits?
Suresh M. Shenoy
4月28日19:58，pete< pfil ... @ mindspring.comwrote：
On 28 Apr., 19:58, pete <pfil...@mindspring.comwrote:
Noob写道：
Noob wrote:
你好，
Hello,
我已经重写了一个函数（greater_or_equal ）依赖于
实现定义的行为和精确宽度
整数的可用性，目标是实现新的实现
（greater_or_equal2 ）可移植到任何平台。
I''ve rewritten a function (greater_or_equal) that relies on
implementation-defined behavior and availability of exact-width
integers, with the goal of making the new implementation
(greater_or_equal2) portable across any platform.
您如何看待新的实施？
（欢迎提出建议和意见。）
What do you think of the new implementation?
(Suggestions and comments are welcome.)
int greater_or_equal（uint16_t u，uint16_t v）
{
return（int16_t）（uv）> = 0;
}
int greater_or_equal(uint16_t u, uint16_t v)
{
return (int16_t)(u-v) >= 0;
}
int greater_or_equal2（unsigned u，unsigned v）
{
return（（uv）& 0xffffU）< = 0x7fffU;
}
int greater_or_equal2(unsigned u, unsigned v)
{
return ((u-v) & 0xffffU) <= 0x7fffU;
}
< OT>
GCC似乎理解源它输出以下代码。
<OT>
GCC seems to "understand" the source as it outputs the following code.
greater_or_equal2：
movl 8（％esp），％edx
cmpw％dx ，4（％esp）
setns％al
movzbl％al，％eax
ret
< / OT>
greater_or_equal2:
movl 8(%esp), %edx
cmpw %dx, 4(%esp)
setns %al
movzbl %al, %eax
ret
</OT>
我不禁要问，它输出的是什么代码：
int greater_or_equal3（unsigned u， unsigned v）
{
return u> = v;
}
I can''t help but wonder, what code does it output for:
int greater_or_equal3(unsigned u, unsigned v)
{
return u >= v;
}
也许OP的代码将用于混淆的
C比赛...
问候Thomas Mertes
Seed7主页： http://seed7.sourceforge.net
Seed7 - 可扩展的编程语言：用户定义的语句
和运算符，抽象数据类型，没有特殊的模板
语法，带接口的OO和多个调度，静态类型，
解释或编译，可移植，在linux / unix / windows下运行。
Maybe the code of the OP will be used in a obfuscated
C contest...
Greetings Thomas Mertes
Seed7 Homepage: http://seed7.sourceforge.net
Seed7 - The extensible programming language: User defined statements
and operators, abstract data types, templates without special
syntax, OO with interfaces and multiple dispatch, statically typed,
interpreted or compiled, portable, runs under linux/unix/windows.
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